The proposed program of research will examine the utility of an information processing framework for exploring the cognitive underpinnings of three neurodevelopmental disorders, autism, Tourette Syndrome, and attention deficit hyperactivity disorder. Previous research has identified a cognitive domain of particular interest in the three disorders, executive function. Unfortunately, previous investigations have relied upon neuropsychological tasks that are cognitively complex and require multiple abilities for successful completion. Such measures are therefore relatively less suitable for exploring the precise nature of the processing deficits underlying the three disorders. An important next step in this field is the development of new measures that decompose complex cognitive functions into more elementary subcomponent operations. Three studies employing information processing tasks will be undertaken to examine three executive functions often confounded in standard neuropsychological measures, inhibition, flexibility, and working memory. The specific aims of these studies are to examine: 1) whether a more fine-grained, differentiated analysis of executive function behaviors can be provided by information processing methodologies; 2) which executive functions are impaired in children with autism, Tourette Syndrome, and attention deficit hyperactivity disorder, respectively; and 3) if we can differentiate autistic children from those with other disorders on the basis of their executive function profiles, as defined by information processing measures. Despite the severity of these conditions, their neurobiological mechanisms and pathophysiology are not yet full understood. The immediate objective of the proposed studies is to identify the specific cognitive deficits associated with the disorders. The long-term goal of the research program is promote future neurobiological investigations by indicating brain regions most fruitful for future study. With more precise specification of the cognitive phenotypes of the disorders, brain structures and functions of particular interest may be identified, thus facilitating the search for the neurobiological origins of the disorders. A better understanding of core cognitive deficits may also lead to improvements in treatment techniques and early identification of at-risk individuals.